The release includes a number of new features that align with the major version number increase. Amongst the major improvements are:

Deep Data support - Pixels can now store a variable-length list of samples. The main rationale behind deep images is to enable the storage of multiple values at different depths for each pixel. OpenEXR 2.0 supports both hard-surface and
volumetric representations for Deep Compositing workflows.

Multi-part Image Files - With OpenEXR 2.0, files can now contain a number of separate, but related, data parts in one file. Access to any part is independent of the others, pixels from parts that are not required in the current operation
don't need to be accessed, resulting in quicker read times when accessing only a subset of channels. The multipart interface also incorporates support for Stereo images where views are stored in separate parts. This makes stereo OpenEXR 2.0 files significantly
faster to work with than the previous multiview support in OpenEXR.

Optimized pixel reading - decoding RGB(A) scanline images has been accelerated on SSE processors providing a significant speedup when reading both old and new format images, including multipart and multiview files.

Namespacing - The library introduces versioned namespaces to avoid conflicts between packages compiled with different versions of the library.

Further information regarding the release, as well as tarball downloads, please visit:
http://www.openexr.com

For the developer community: the source code has been tagged as "v2.0.0.GM" and the master branch is now pointing to this.
https://github.com/openexr/openexr